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February 1-3, 2007 Reaching Beyond Our Borders 2007 Conference, US-ISPO in cooperation with The O&P Edge, Hyatt Regency Cancun, Cancun, MX. Contact: Dianne Farabi, +1 614.659.0197; e-mail: firstname.lastname@example.org, website: www.reachingbeyondourborders.org March 21-24, 2007 American Academy of Orthotists and Prosthetists Annual Meeting and Scientific Symposium, San Francisco Marriott, San Francisco, CA. Contact: Diane Ragusa, +1 703.836.0788; email: email@example.com, website: www.oandp.org June 15-17, 2007 Amputee Coalition of America: Annual Educational Conference & Exposition, Renaissance Waverly Hotel, Atlanta, GA. The ACA holds an annual national conference which facilitates informational sessions on health and advocacy, offers special events such as discussion groups and parties. Contact: lan Young, +1 888.267.5669; e-mail: firstname.lastname@example.org Prosthetics
G. M. Street ion dit Ey ish terl gl En uar Q Vacuum Suspension and its Effects on the Limb
Since its inception in 1999 (Board et al., 2001), vacuum suspension has proven to be a major innovation. Vacuum suspension provides the amputee with unmatched linkage. This linkage alters the pressures that the limb experiences, which in turn prevents daily limb volume loss and improves limb health. The purpose of this paper is to review what is known about vacuum suspension and its effects on the limb. Vacuum Suspension
A vacuum pump removes air molecules from the thin, sealed air space (sheath) between the total surface weight bearing socket and liner as shown in Fig. 1. The vacuum created by the removal of these air molecules holds the liner firmly and globally to the socket wall as shown in Fig. 2a. Note that the limb is completely isolated from the vacuum. This Imprint
Published by Bundesinnungsverband für Orthopädie-Technik / Verlag Orthopädie-Technik Reinoldistr. 7-9 44135 Dortmund, Germany Tel.: +49 (0)231 / 55 70 50-50 Fax: +49 (0)231 / 55 70 50-70 E-mail: email@example.com Edited by Dirk Böcker Published quarterly providing articles from Orthopädie-Technik, German edition, © Bundesinnungsverband 2006 Orthopädie-Technik Quarterly, English edition IV/2006 raises the question: How can this “The second major bonus is how 2001; Goswami et al., 2003) and vacuum that is completely isolated well your device stays ‘glued’ to my patients continue to consistently from the limb affect it in any way? leg, making the prosthesis feel much identify daily volume maintenance The answer to this question is lighter and allowing me to wear work as a major advantage of vacuum addressed in detail later in this boots again. The previous system that suspension. paper. However, the essence is that locked the liner to the socket with a A study comparing daily limb the liner, and therefore skin, are no pin always felt heavy, and made work volume loss between valve and longer able to separate from the boots unbearable. Managing my horse vacuum suspension showed that socket. This lack of separation of farm with tennis shoes was often a limbs of trans-tibial amputees lost challenge, particularly in the muddy an average 6.5% in volume during the liner and limb from the socket months. Now work boots feel light, 30 minutes of walking with valve is thought to explain why vacuum and are easy to walk in.” suspension. On a separate day, the suspension prevents volume loss same subjects in the and improves limb same sockets, except health. with vacuum applied to As shown in Figure 2b, the expulsion port (vacuthe sum of the axial um suspension), gained components of the liner 3.7% in volume while anchoring forces creates walking. In a separate an exceptionally large study (Goswami et al., suspension force; ~70 kg 2003), it was again for the average size limb shown that vacuum sus(33 cm proximal circumpension prevents daily ference) and vacuum (-78 volume loss or results in kPa) (Street, 2006). This a slight gain. means that it would take Limb volume flucan extraction force of ~70 tuates as pressure fluctukg to cause any ates (Guyton, 2000). In separation between the the morning before liner and socket. Since donning the socket, with extraction forces during one atmosphere of daily activities seldom pressure (1 atm), limb exceed 5-10 kg, vacuum volume is stable. As limb suspension prevents sepapressure increases, for ration between the liner example after donning and socket (Board et al., the undersized socket or 2001). This is in sharp during stance, the limb contrast to all other loses volume. Volume is modes of suspension lost because elevated (>1 where the liner separates atm) pressure increases from the socket as soon as the amount of interstitial even a small extraction Fig. 1 Cross section of vacuum suspension system showing sealed air force (<0.25 kg) is applied space (sheath). Note that the sealed air space does not extend to the fluid being driven back to the socket. thigh. The seal between the top of the liner and sealing sleeve isolates into the bloodstream and the limb from the vacuum. lymphatic vessels, and out of the limb. In Proprioception contrast, as pressure drops below 1 and Prosthesis Control atm, such as when the tibia Limb Volume extracts and causes the soft tissues to elongate during swing, the limb Eliminating separation between Vacuum suspension further gains volume. Volume is gained the liner and socket improves the improves proprioception and because low (<1 atm) pressure patient’s spatial awareness of control of the prosthesis by increases the amount of fluid being (proprioception) and control over preventing the limb from losing drawn out of the blood stream and the prosthetic leg. Amputees new volume during the day. Unlike all into the limb’s tissues. to vacuum suspension typically other modes of suspension where Hence, there are three possible express surprise at how the prosthe limb loses volume each day explanations for why vacuum thesis feels more a part of the limb. and causes a sloppy fit, the limb suspension prevents daily volume The prosthetic leg is more responsstays hydrated and positively loss in ambulating amputees: 1) ive; as the amputee moves his/her keyed to the socket. less fluid is driven out of the limb limb there is a corresponding, The first trans-tibial amputees to because of a reduction in positive immediate movement of the prosuse vacuum suspension in 1999 pressure during stance, 2) more thetic leg. The following unsolireported that their limbs no longer fluid is drawn into the limb cited quote from an amputee that lost volume during the day. This because of a decrease in pressure switched to vacuum suspension unanticipated effect of vacuum during swing or 3) both. Beil et al. illustrates the functional signifisuspension has since been con(2002) found that both changes cance of the improved linkage. firmed in two studies (Board et al.,
Orthopädie-Technik Quarterly, English edition IV/2006 3 occur with vacuum suspension. was able to make that appointment, I Limb Health Compared to valve suspension, was called in by my prosthetist to try vacuum suspension 1) reduces the There is considerable anecdotal something new…your device. Within external positive pressure by ~4-7% evidence from amputees that 2 weeks of wearing the [vacuum during stance and 2) increases the shows vacuum suspension suspension] system, the pressure sores drop in pressure an additional improves limb health. A few had completely healed. For the first ~27% during swing. So, vacuum clinical studies, yet to be time I can wear my leg all day in suspension shifts the fluid balance published, are underway to comfort. I used to go to bed for 2 hours in the limb to one of maintenance document this effect. A nearly as soon as I got home from work to or slight gain by driving less fluid universal observation with vacuum give my stump a much needed break out of the limb during stance and suspension is the reduction or from the pressure. Last evening, after drawing more fluid in during elimination of minor skin a 12-hour day at work, I stood in the swing. Of these two, Beil et al. problems such as folliculitis and kitchen and made supper for my (2002) proposed that drawing recurring cysts. More impressive family, and then did some work before more fluid in because of the are the cases where open wounds calling it a night. Your innovation is additional 27% drop in pressure is heal and remain healed upon nothing short of miraculous.” probably most responsible for switching to vacuum suspension. All prostheses place the limb in volume maintenance. an unhealthy environWe hypothesize that ment. The skin is subthis additional 27% drop jected to pressures and in pressure is a result of shear forces that exceed the liner staying those for which it is anchored to the socket normally designed to and the skin staying in withstand. Furthermore, close contact with the the warm, moist socket liner. With the liner environment is conduglobally anchored, as the cive for microbial tibia extracts from the growth; thus challenging soft tissues during swing, the limb’s immune the tissues elongate and system. Vacuum suspentissue pressure drops to a sion has reduced the greater extent than with peak pressures (Beil et al., other modes of sus2002) and shear forces pension (Beil et al., because of its superior 2002). With valve suslinkage and its mainpension, the liner/limb tenance of limb volume. separate from the socket Vacuum suspension has (Street, 2006); resulting in put an end to the abusive less tissue elongation, cycle where the fit smaller drop in pressure Fig. 2 The vacuum creates forces that: a) anchor the liner to the becomes sloppy as the socket. The sum of all the axial components of the axial forces creates and less fluid being a large: b) suspension force of ~70 kg. The suspension force prevents limb loses volume, drawn into the limb. the liner/limb from extracting out of the socket. causing the limb to With pin suspension, hammer and bell clap in there is an interesting paradox. It should be emphasized that this the socket, which in turn causes During swing, there is an even healing occurs while the amputee even more volume loss and limb larger pressure drop than with wears the vacuum suspension trauma. The warm, moist socket vacuum suspension; an additional prosthesis. In contrast, other environment remains an un9% at the distal end of the limb resolved problem for all modes of modes of suspension normally (Beil et al., 2002, Beil and Street, suspension. require the limb be out of the 2004). Aside from less physical abuse, a prosthesis for healing to take place. The paradox is that while pin second likely explanation for the The following unsolicited quote suspension is even more forceful in observed improvement in limb illustrates a typical experience of drawing fluids into the limb, it is an amputee with chronic wounds health and wound healing with only at the distal end of the limb after switching from pin to vacuum suspension is increased while the proximal portion of the blood flow (Street, 2002). Skin vacuum suspension. limb is squeezed. So, with pin blood flow was measured as “I have been a left below knee suspension, instead of moderate simulated walking pressures were amputee for 3 years, and for most of (valve suspension) to strong applied to the limb. The cyclic, that time struggled with pressure (vacuum suspension) global filling positive and negative pressures sores. Late last summer I developed of the limb, there is strong distal measured in an earlier study (Beil two pressure sores on my distal stump filling, with a predisposition for et al., 2002) were applied to the that progressed into full-thickness congestion of these fluids and limb to simulate vacuum suspenserosions. I suffered with these painful volume loss proximally because of ion. A clear pumping effect was sores for over 3 months before my the simultaneous proximal observed in all trials. During doctor recommended that I have squeeze. simulated stance, blood was driven plastic surgery to resect them. Before I 4
Orthopädie-Technik Quarterly, English edition IV/2006 References  Beil, T.L. and Street, G.M. (2004). Comparison of interface pressures with pin and suction suspension systems. Journal of Rehabilitation Research and Development, 41(6A), 821-828.  Beil, T.L., Street, G.M. and Covey, S.J. (2002). Interface pressures during ambulation using suction and vacuum-assisted prosthetic sockets. Journal of Rehabilitation Research and Development, 39(6), 693-700.  Board, W.J., Street, G.M. and Caspers, C. (2001). A comparison of trans-tibial amputee suction and vacuum socket conditions. Prosthetics and Orthotics International, 25, 202-209.  Goswami J., Lynn R., Street G., Harlander M. (2003). Walking in a vacuum-assisted socket shifts the stump fluid balance. Prosthetics and Orthotics International, 23, 107-113.  Grevsten, S. (1977). Patellar tendon bearing suction prosthesis. Upsala Journal of Medicine and Science, 72, 209-220.  Grevsten, S. and Marsh, L. (1971). Suction-type prosthesis for below- knee amputees, a preliminary report. Artificial Limbs, 15, 78-80.  Guyton, A.C. and Hall, J.E. (2000). Textbook of medical physiology. 10th edition, London, W.B. Saunders Co.  Street, G.M. (October 2002). Effect of simulated socket pressures on skin blood flow. American Academy of Orthotists and Prosthetists Annual Meeting, Chicago, IL, USA.  Street, G.M. (May 2006). Benefits of vacuum suspension. World Congress Orthopadie + RehaTechnik, Leipzig, Germany. out of the skin blood vessels because of positive pressure. During simulated swing, the vessels rapidly refilled as the limb was exposed to negative pressure. As of yet, no studies have been conducted to show that the increased blood flow improves limb health. However, it would have the potential to do so since blood is the delivery system that provides the limb with its nutrients and immune cells, and removes wastes. This coupled with the knowledge that vacuum suspension enhances fluid and nutrient exchange in the soft tissues strongly suggests that circulatory changes play a role in improving limb health and wound healing. Enhanced fluid exchange is thought to exist because of the observed limb volume maintenance as previously discussed. The potential improvements in limb health and wound healing due to the global increase in blood flow and fluid exchange are probably most important when comparing vacuum suspension to pin suspension. Pin suspension creates a relatively strong distal draw while simultaneously constricting the limb proximally during swing phase (Beil and Street, 2004). This has the potential of causing distal limb congestion. In contrast, the pumping effect seen with vacuum suspension and valve suspension (to a lesser extent) appears to increase global circulation and fluid exchange, and avoid congestion. 6 Importance of Proper Fit
The benefits of vacuum suspension are only realized by the amputee if the limb and liner are in total contact with the socket. Meeting this requirement depends on the actions of the prosthetist and amputee. The prosthetist must design and construct a total surface weight bearing socket that closely matches the shape of the amputee’s limb, and is free of specific weight bearing structures and areas of relief. The amputee must maintain total contact by adding fillers if the limb loses volume. If both the prosthetist and amputee meet this requirement and vacuum is maintained, the amputee will reap the benefits of vacuum suspension. If they fail to meet this requirement, the limb will experience pressure, and skin damage in extreme cases, as the liner and limb are pulled into the void. A properly fitting vacuum suspension system is almost certainly the healthiest environment for all limbs. This is especially true for vascular amputees or those on anticoagulants (“blood thinner” medication) who are prone to internal bleeding when exposed to high or low pressures and shear forces. Vacuum suspension minimizes these pressures and shear forces because of the limb’s positive global connection with the socket; a connection that is maintained throughout the day since limb volume is maintained. Old Idea Revisited
Removing air molecules from the air space (sheath) between the socket and liner is a new concept. Yet, having the limb staying in close contact with the socket, and observing that it improves linkage and heals wounds is not new. Grevsten and Marsh (1971) and Grevsten (1977), who used a prosthesis with trans-tibial amputees that closely mimics vacuum suspension, reported that “all of the patients feel that the prosthesis is identified more closely with the lower leg” and that “all patients who were unable to wear the ordinary PTB prosthesis because of a skin lesion and who then tried the PTB-suction model noticed healing while using the new prosthesis.” Grevsten and Marsh (1971) used a total contact, undersized socket. The trans-tibial amputee’s limb was pulled into the socket using a stocking. After pulling the limb into the socket, the stocking continued to be pulled out the distal port until the limb was left in total contact with the socket. The hole was sealed with a threaded plug. Since there was virtually no air in the socket, suction prevented any measurable separation between the skin and socket. So, as with vacuum suspension where the skin stays in close contact with the anchored liner, their suction system where the skin was held in close contact with socket demonstrated similar improvements in linkage and healing of wounds.
Orthopädie-Technik Quarterly, English edition IV/2006 Summary
Vacuum suspension is simply the removal of air molecules from the sealed air space in a valve suspension system. The resulting vacuum has one direct physical effect; it anchors the liner to the socket. The large suspension force, ~70 kg, created by the axial components of the liner anchoring forces prevents separation between the liner and socket. This provides the amputee with unmatched linkage that improves his/her spatial awareness and control over the prosthesis. With this elimination of pistoning, limb pressures and shear forces are reduced, providing the limb with a healthier environment. Unlike all other modes of suspension, vacuum suspension prevents the limb from losing volume during the day. So, a healthier environment is main- tained throughout the day. The global pumping effect of the cyclic positive and negative pressures during walking increases circulation and fluid exchange, and probably plays a role in improving limb health and wound healing. Acknowledgements
I wish to thank the following former graduate students for their ground breaking research that improved our understanding of vacuum suspension and made this paper possible: Wayne Board, Tracy Beil, Jaideep Goswami and Marie Harlander. Thanks are also extended to the inventor of vacuum suspension, Carl Caspers, for his unwavering commitment to improving the lives of amputees, keen insight and friendship. I am also in debt to the many amputees and prosthetists; too numerous to mention here, that have been willing to share their practical knowledge about prosthetics. Finally, I would like to thank my gifted and genuinely curious colleague, David Bacharach, for always taking the time and having the interest in helping our research team “get to the essence of things.” Author contact information: Glenn M. Street, PhD Human Performance Laboratory HAH 111 St. Cloud State University St. Cloud, MN 56301 USA E-Mail: firstname.lastname@example.org Orthopädie-Technik Quarterly, English edition IV/2006 7 ...
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